Chemistry of the Nanomaterial Interface: Controlling Nanoparticle Morphology, Self-Assembly, and Catalysis

Nanomaterials present a suite of properties that are advantageous for broad applications in the catalytic processes that will solve our energy requirements in the next century and beyond. They have a large surface area to volume ratio, maximizing the use of materials, and often have unique reactivities relative to their bulk counterparts. Moreover, colloidal chemistry approaches in recent decades have advanced to a stage where many unique and robust approaches to precisely control parameters such as size, shape, and composition exist. This tunability provides excellent model systems for studying heterogeneous catalysis in real conditions to optimize catalytic output by generating relationships between the well-defined nanomaterial structure and the activity.

The ability of nanomaterials to form these precisely controlled structures and to perform desired catalytic reactions are dictated by their surface chemistries. The binding of molecules to stabilize the surface directly impacts the final structure of the nanomaterial. Interactions of reaction intermediates with the surface dictate how successfully the material will catalyze a given reaction. The goal of this dissertation is to explore the surface chemistries of various nanomaterials through experimental and theoretical means to understand how these interactions influence nanoparticle morphology and improve catalytic activity.

For nanomaterial synthesis, the importance of surfactants and other chemical additives in producing anisotropic nanoparticles is explored in brookite TiO2 and late transition metal systems by application of Density Functional Theory (DFT). Furthermore, atomically precise rare earth oxides superlattices are generated by a self-assembly method driven by high-temperature surface ligand switching. Molecular dynamics simulations show the favorability of this switch and point to the interactions that generate the assembly.

For exploring nanomaterial catalysis, surface chemistry of catalytic intermediates is probed through DFT methods for CO2 reduction over AgPd alloy nanoparticles and hydrogen evolution reaction over Ir-Co2P nanoparticles. Surface enhanced infrared absorption spectroscopy (SEIRAS) is shown as an experimental probe for direct observation of reaction intermediates in the ethanol oxidation reaction. Each of these works derives information about how the surface strain, ligand, and ensemble effects influence catalysis over nanomaterials.